According to ESRB, this game contains: Blood, Violence
Parents should know that the game has a lot of killing, but this is primarily of undead monsters, and I didn't think it was terribly gruesome. I was honestly a little surprised by the rating; this game has nowhere near the level of violence or disturbing content of games like Silent Hill or Grand Theft Auto. Personally, I'd have no trouble letting a teenage child of mine play this game.
Fans of Castlevania will be the hardest to please. I think the game is good, and it does stay true to the series hack-n-slash; but it lacks the magic that the recent handheld iterations seem to keep. Perhaps Castlevania is best served in 2D.
Deaf and Hard of Hearing Gamers shouldn't run into problems, thanks to subtitles for dialog.